Oxygen-enriched hierarchical porous carbon derived from biowaste sunflower heads for high-performance supercapacitors

Sunflower heads, a biowaste from sunflower crop, was first explored as a sustainable precursor to synthesize porous carbon (PC) as a supercapacitor electrode material. Here we report the preparation of oxygen-enriched PC by the simple and low-cost carbonization of sunflower heads followed by KOH activation. The resulting carbon has a hierarchical pore structure comprised of abundant micropores and mesopores, a specific surface area of 1032 m(2) g(-1) and a high oxygen content of 21 wt%. Due to the above unique porous nature and oxygen enrichment, the sunflower head carbon (SFHCs) exhibits a high specific capacitance of 345 F g(-1) at 1 A g(-1) in 6 M KOH aqueous electrolyte and shows considerable rate capability with a retention of 81% at 20 A g(-1). Moreover, the SFHCs symmetric supercapacitor delivers a high energy density of 9.2 W h kg(-1) at a power output of 482 W kg(-1). This study first introduces the utilization of biowaste sunflower heads as a renewable precursor to prepare high value-added porous carbon for high performance supercapacitors.